Sciencemadness Discussion Board

Chemical Resistance of Stoppers

Yttrium2 - 18-3-2018 at 09:16

Which bungs / Stoppers are best?

Which have the most chemical Resistance?

Or, which material stopper is used for what?

DavidJR - 18-3-2018 at 09:25

Ground glass stoppers are best.

Morgan - 18-3-2018 at 10:00

Well I bought a bunch of rubber stoppers with no holes, one, and two holes and over time they started to sweat an oily substance and aside from that they are now hard. Maybe putting them in bags and keeping them in the garage in summer did it.
So for some things these silicone stoppers are better like higher temperatures but they aren't good for some chemicals. I don't like the way the black rubber stoppers smell, thus I kept them outside. And it's a hassle if you don't have the right size so I forced myself to buy a bunch of sizes once again. Here's some larger sizes of the silicone stoppers atop my freezer in the garage. These stoppers smell too though, but maybe over time the odor will fade.
https://www.ebay.com/itm/80pc-1-16-3-4-High-Temp-Silicone-Ru...

DSC_0002 (1).JPG - 220kB DSC_0003.JPG - 231kB

[Edited on 18-3-2018 by Morgan]

Magpie - 18-3-2018 at 10:21

I usually buy EPDM. For best chemical and heat resistance I use Viton.

Akhil jain - 18-3-2018 at 11:38

It is best to use rubber stoppers since holes can be dig in it ,they are air tight and cheap.
But if you are making nitric acid you can't use rubber stoppers since nitric acid attacks rubber. In this preparation whole apparatus is made of glass

BromicAcid - 18-3-2018 at 11:46

Once upon a time, cork stoppers were about all that was available. Older literature however is able to use them for many applications by treating them with the appropriate compound (waterglass, shellac, bitumen, etc). On the plus side they are cheap.

metalresearcher - 18-3-2018 at 11:54

Quote: Originally posted by Akhil jain  
It is best to use rubber stoppers since holes can be dig in it ,they are air tight and cheap.
But if you are making nitric acid you can't use rubber stoppers since nitric acid attacks rubber. In this preparation whole apparatus is made of glass


However, this is a tedious job. Same with silicone stoppers. Simply using a cordless drill is not an option as the hole drilled jumps back as it is too elastic. Even when the drill bit is 2mm larger than the diameter of the tube to be used.

Akhil jain - 18-3-2018 at 11:58

It is not a tedious job to make holes in rubber stoppers
If you have a cork borer it is very easy if you have a drill it's still easy. You can even drill two holes and pass two delivery tubes in it . Use rubber stoppers if you don't want your gases to leak out . It is easy to work with rubber stoppers than glass ones

Magpie - 18-3-2018 at 12:00

I use one of those “cork borers” to bore holes in the rubber.

Akhil jain - 18-3-2018 at 12:01

Quote: Originally posted by Morgan  
Well I bought a bunch of rubber stoppers with no holes, one, and two holes and over time they started to sweat an oily substance and aside from that they are now hard. Maybe putting them in bags and keeping them in the garage in summer did it.
So for some things these silicone stoppers are better like higher temperatures but they aren't good for some chemicals. I don't like the way the black rubber stoppers smell, thus I kept them outside. And it's a hassle if you don't have the right size so I forced myself to buy a bunch of sizes once again. Here's some larger sizes of the silicone stoppers atop my freezer in the gara



[Edited on 18-3-2018 by Morgan]

Can I use silicon stoppers for making nitric acid . Won't they be attacked by fuming HNO3

Sulaiman - 18-3-2018 at 12:19

For boring holes through corks and red rubber bungs, I have similar to these
https://www.ebay.co.uk/itm/Ajax-Scientific-6-Piece-Brass-Cor...
but I rarely use them.
There are matching sharpeners https://www.ebay.co.uk/itm/RVFM-Cork-Borer-Sharpener/1223699...

Magpie - 18-3-2018 at 13:14

I use my borers all the time. Thanks Sulaiman for the link to the sharpeners, I just bought one off Amazon.

symboom - 18-3-2018 at 14:02

Could rubber stoppers be coated in teflon spray to proteck them from corrosive compounds suchbas rubber desolving solvents and strong acids

phlogiston - 18-3-2018 at 14:28

Quote: Originally posted by metalresearcher  

However, this is a tedious job. Same with silicone stoppers. Simply using a cordless drill is not an option as the hole drilled jumps back as it is too elastic. Even when the drill bit is 2mm larger than the diameter of the tube to be used.


Freeze the rubber prior to drilling.
Ben Krasnow (Applied Science) has a video on machining frozen rubber with a cnc router.

Yttrium2 - 18-3-2018 at 14:35

Quote: Originally posted by metalresearcher  
Quote: Originally posted by Akhil jain  
It is best to use rubber stoppers since holes can be dig in it ,they are air tight and cheap.
But if you are making nitric acid you can't use rubber stoppers since nitric acid attacks rubber. In this preparation whole apparatus is made of glass


However, this is a tedious job. Same with silicone stoppers. Simply using a cordless drill is not an option as the hole drilled jumps back as it is too elastic. Even when the drill bit is 2mm larger than the diameter of the tube to be used.



They have drill bits for rubber stopper

Sulaiman - 18-3-2018 at 15:46

Quote: Originally posted by Magpie  
I use my borers all the time.


So do you bear "the mark of the chemist" ?

Magpie - 18-3-2018 at 15:53

No marks except on my wood bench. I now place a piece of sacrificial wood under the stopper when boring. I also wear leather gloves.

Morgan - 18-3-2018 at 17:43

I saw this but just wonder how a brad point drill bit would work?

How to drill a hole into a rubber stopper
https://www.youtube.com/watch?v=S9Webmd9Jvw

https://www.toolstoday.com/g-22-the-brad-point-boring-bit

LearnedAmateur - 19-3-2018 at 00:12

I use orange rubber stoppers mostly, got a couple of glass ones too which are obviously fine for the majority of applications, but rubber is attacked by a lot of solvents over time. I’ve noticed that when stoppering a flask containing ethanol, isopropanol, toluene etc. They tend to swell and ‘wet’ bits will flake off. I’ve ended up having these bits floating around in the mixture/solvent when they’re removed before.

XeonTheMGPony - 19-3-2018 at 03:36

I've applied a gentle layer of silicon grease then wrapped in teflon tape the stoppers when I had to use them for harsh reactions and it seems to have don the job on most of them for most of the time, rubber is a crap material IMO hardens over time, can fuse to the glass in certain conditions, cheap rubbers smell bad.

They had their time, I prefer to use glass gas inlets and such failing that chemically treated cork wold be preferable to rubber!

I never used silicon befor but knowing the material I'd say it'd be better.

Then there is machined teflon stoppers one can get.